I. A TD-HSPA+ Continuous Packet Connectivity
3GPP R8 (the 3rd generation partnership project, release 8) incorporates an HSPA+ (high speed packet access enhanced) technology into a TD-SCDMA (time division-synchronous code division multiple access) protocol. The TD-HSPA+ technology is the upgrading regarding an original HSPA technology, mainly for increasing user capacity and throughput of a system, and optimizing the support for a data service of “consistently online”.
The TD-HSPA+ is a set of multiple enhanced technologies, comprising two aspects of enhancing physical layer and enhancing high layer. Technology of enhancing physical layer comprises a high order modulation, such as a 64QAM (quadrate amplitude modulation), MIMO (multiple-input multiple-out-put) and a multicarrier technology. Technology of enhancing high layer comprises enhanced CELL_FACH (cell forward access channel), enhanced layer 2 and CPC (continuous packet connectivity).
The CPC refers to “always online” of a packet user. The CPC enables, by improving the HSPA function of 3GPP R5/R6, the packet user having continuous connectivity requirements to be able to avoid bringing more expenses and time delay caused by frequent re-establishment, thus achieving the purpose of increasing the number of the packet users in the CELL-DCH (cell dedicated channel) state, increasing user capacity and system efficiency of the VoIP (voice over internet protocol).
A semi-persistent resource is incorporated into the CPC; the semi-persistent resource is valid for a long time after being configured by a NodeB; and a terminal device performs data receiving and transmitting according to an Rx mode or Tx mode configured by the NodeB. Configuration of the semi-persistent resource may be semi-static configuration and dynamic configuration. The semi-static configuration is that the terminal device is configured by an RNC (radio network controller) via an RRC (radio resource control) message in the form of a list; while the dynamic configuration is that the terminal device is configured by the NodeB via a downlink HS-SCCH (high speed shared control channel) or an uplink E-AGCH (enhanced absolute grant channel). The terminal device comprehensively obtains specific semi-persistent resource configuration of the terminal device according to dynamic properties in combination with the semi-static configuration.
For reducing power expenses of a control channel, a control channel DRX (discontinuous reception) operation is also incorporated into the CPC. The control channel DRX operation is divided into HS-SCCH DRX and E-AGCH DRX performing independently. When the system confirms that it is unnecessary for the terminal device to monitor an HS-SCCH or E-AGCH channel within a relatively long interval, the NodeB will inform the terminal device to enter a control channel DRX state by means of a timer or command, at this moment, the terminal device only needs to receive a corresponding control channel at a fixed period and time offset.
II. Automatic Gain Control
In general, an input signal of a receiver has a great dynamical variation; and the purpose of AGC (automatic gain control) is to make an output signal normalized and to be kept at a relatively stable level. FIG. 1 is a basic schematic diagram showing controlling a gain via an AGC feedback loop in the traditional art. As shown in FIG. 1 an AGC control unit and a VGA (variable gain amplifier) constitute a feedback loop. I and Q signals before being filtered by a baseband are input in the feedback loop, power accumulation and average processing are performed within a period of time, then it is compared with a reference power value; an error obtained by comparing is sent to a filter of the feedback loop, and is filtered and output to the AGC control unit via the filter; and finally the AGC control unit generates gain adjustment of the VGA and LNA (low noise amplifier).
In an actual TD-SCDMA terminal receiver system, since there is a time delay in calculation processing of the AGC control unit, in general, a gain (an AGC reference value) obtained by calculation of a signal received from a certain channel last time controls a gain of a signal received from the same channel the next time. Because of fast time varying characteristics of a wireless channel, a reception interval between two signals successively received from the same channel should not be too large. In a conventional HSPA technology, in general, the interval is merely several sub-frames.
III. Problems Facing the AGC in a TD-HSPA+ CPC State
AGC control in a CPC state is different. Taking CPC transmission of HSDPA (high speed downlink packet access) as an example, a terminal device uses a set of resource patterns (containing parameters such as a repetition period and a repetition length) configured by a NodeB to receive an HS-DSCH (high-speed downlink shared channel) signal, and it is unnecessary to be scheduled by HS-SCCH signalling on a frame-by-frame basis. In a semi-persistent resource pattern specified in the protocol, the longest repetition period may reach 32 sub-frames, i.e. a reception interval between two signals successively received from a CPC HS-DSCH may reach 32 sub-frames.
Although the NodeB may amend a semi-persistent resource via HS-SCCH signalling (reconfiguring HS-SCCH), when HS-SCCH DRX is not used, sending time of reconfiguring HS-SCCH is not fixed. An interval between two times of reconfiguration of the HS-SCCH may also be very long, for example, in a typical network configuration, the interval may reach 40 sub-frames. During this time, the terminal device must continuously monitor whether there is reconfiguration HS-SCCH signalling issued on an HS-SCCH physical resource allocated thereto.
In the above-mentioned scenarios, since the interval between two signals successively received from the CPC HS-DSCH or two reconfiguring HS-SCCH signalings may be very long, a signal power may have a drastic variation during the interval. If an AGC reference value obtained by calculation of a signal received last time is directly used to control a gain of a signal received this time, the problem that the present gain can not reflect an actual signal power variation may occur, which results in that a signal converted by the terminal device is saturate or an amplitude value of the terminal device is too small, thus losing downlink data or missing critical reconfiguration scheduling information, and affecting the performance of the terminal device, such as a receiver.